How to use while loop inside subshell after pipe - bash

Question

I have looked and looked for a solution to this, but I can't find anything that directly addresses my problem. I'm trying to add up the lines added and removed by certain authors in a git repo. I'm using git log piped to sed piped to awk which I am now trying to pipe to a subshell to add up the numbers. The issue is that the piped input isn't getting interpreted properly in the subshell, and I can't figure out why. I suspect it's in the while-loop, because of the nature of subshell syntax and its pickiness with semicolons.
I've moved around the code inside the subshell, added and removed semicolons, used backslashes for line separation to see if that was the issue, and none of it has worked. I'm not well-versed in shell so it could be a glaringly obvious issue to someone who is more experienced. "$author" is just the nth positional parameter from the command-line.
for author; do
echo "Listing file and line changes for $author"
git log --shortstat --author="$author" ${date:+--since="$date"} \
| sed -n -e '/files\? changed/s/, /\n/gp' \
| awk '
$3=="changed" {changed+=$1}
$2=="deletions(-)" {deletions+=$1}
$2=="insertions(+)" {insertions+=$1}
END{
print "files changed:", changed,
" lines removed:", deletions,
" lines added:", insertions,
" net change:", insertions-deletions
}'
done | {
total_changed=0
total_added=0
total_removed=0
while read changed insertions deletions; do
let total_changed+=changed
let total_added+=insertions
let total_removed+=deletions
done
echo "totals:"
echo "files changed: $total_changed"
echo "lines added: $total_added"
echo "lines removed: $total_removed" ;
}
The last part should output the totals but instead they output 0. I also get some weird syntax errors. Here's the output (input is "Benjamin Hills):
/home/bhills/./git-log-lines-removed.sh: line 65: let: and line changes for Benjamin Hills: syntax error in expression (error token is "line changes for Benjamin Hills")
/home/bhills/./git-log-lines-removed.sh: line 64: let: changed:: syntax error in expression (error token is ":")
/home/bhills/./git-log-lines-removed.sh: line 65: let: 61 lines removed: 1345 lines added: 246 net change: -1099: syntax error in expression (error token is "lines removed: 1345 lines added: 246 net change: -1099")
totals:
files changed: 0
lines added: 0
lines removed: 0

Answer 1

Your code is trying to generate human-readable output twice: Once in awk, another time in bash. Since the output awk generates is input to bash, that means you're trying to pipe an output format meant for humans and read it as if it were an input format meant for machines; obviously, it's not.
There's no good reason to take that approach at all: Generate all your human-readable output in the same process.
#!/usr/bin/env bash
# ^^^^- NOT /bin/sh
total_changed=0
total_deletions=0
total_insertions=0
for author; do
changed=0; deletions=0; insertions=0
# Loop over output from "git log" for a single author
while read added deleted _; do
(( ++changed )) # each line is a file changed
{ [[ $added = - ]] || [[ $deleted = - ]]; } && continue # skip binary files
(( insertions += added ))
(( deletions += deleted ))
done < <(git log --numstat --format='' --author="$author" ${date:+--since="$date"})
# Print results from that author
printf '%s\n' "For author: $author" \
" Files changed: $changed" \
" Deletions: $deletions" \
" Insertions: $insertions"
# Add to totals
(( total_changed+=changed ))
(( total_deletions+=deletions ))
(( total_insertions+=insertions ))
done
# Print those totals
printf '%s\n' "Totals:" \
" Files changed: $total_changed" \
" Deletions: $total_deletions" \
" Insertions: $total_insertions"